libobs/util: Do not ignore deprecation on windows

On MSVC, deprecated types/functions were being completely ignored by the
compiler due to this pragma.  Any plugins/programs that depended on this
would also have this warning disabled due to it being in this file.
This pragma was most likely originally done due to the MSVC warnings for
C-standard functions, which are now ignored via _CRT_SECURE_NO_WARNINGS
on all projects instead.